Currently, research into transistors having a Silicon On Insulator (SOI) structure is actively progressing. The SOI structure includes a lower semiconductor substrate, an upper silicon pattern and a buried insulating layer interposed between the lower semiconductor substrate and the upper silicon pattern to insulate them from each other. Transistors having the SOI structure can realize high-speed operation and reduced power consumption. However, the transistors having the SOI structure may have difficulty in controlling threshold voltage.
Meanwhile, an SOI Metal Oxide Semiconductor Field-Effect Transistor (MOSFET) employing a back gate to control threshold voltage of transistors having the SOI structure is discussed in, for example, U.S. Pat. No. 6,664,598 B1 entitled “Polysilicon Back-Gated SOI MOSFET for Dynamic Threshold Voltage Control” to Dennard et al.